When NASA's Nancy Grace Roman Space Telescope lifts off, it will peer into vast stretches of the Milky Way that have never been thoroughly searched for planets — and scientists estimate it could uncover roughly 100,000 previously unknown worlds in the process, more than fifteen times the nearly 6,300 exoplanets discovered so far through all existing NASA missions and observatories combined.
What makes this discovery potential so profound is not just the sheer number, but where Roman will look. Nearly every exoplanet found to date has come from our cosmic neighborhood, those relatively nearby stars within a few thousand light years of Earth. Roman, however, will extend the hunt far beyond that familiar ground, scanning the Milky Way's densely packed central bulge and reaching all the way to the far side of the galaxy. This shift in perspective could fundamentally reshape our understanding of how planetary systems form and evolve across different galactic environments.
"Our galaxy is home to a variety of different environments, but when it comes to hunting for exoplanets, we've really only explored one: our own neighborhood," said Elisa Quintana, an exoplanet researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Quintana leads a team building software and simulations to prepare for Roman's exoplanet observations. "Roman will extend the search far enough to encompass other galactic habitats, which could help us learn how planet formation varies across different regions of the Milky Way."
Roman will employ two complementary detection techniques to capture this unprecedented planetary census. The transit method, expected to discover roughly 100,000 worlds, works by measuring the tiny dip in starlight when a planet passes in front of its star. This approach is particularly sensitive to large, extremely hot planets that block significant amounts of light and complete their orbits frequently. The second technique, called microlensing, uses the gravity of foreground stars and their planets to magnify light from distant background stars, making them appear briefly brighter. This method is expected to reveal more than 1,000 worlds and excels at finding smaller planets far from their stars—worlds as small as Earth and Mars, including those within habitable zones. Crucially, many of these distant planets would be nearly impossible to detect using other methods.
The full picture Roman will provide could help solve one of astronomy's lingering mysteries: where our own solar system really came from. Today, Earth orbits roughly 27,000 light years from the galactic center, but researchers believe the solar system likely formed about 10,000 light years closer in before gradually drifting outward. Evidence comes from the Sun's chemical composition—specifically, its abundance of heavy elements like silicon, oxygen, and magnesium.
Here's the key insight: stars located closer to the galactic bulge are older and contain more heavy elements, while stars in the galaxy's outer regions tend to have fewer. These chemical differences appear to influence the types of planets that form around stars. Research already shows that stars with more heavy elements tend to host more planets, especially giant ones. By examining entirely different stellar and planetary populations across the Milky Way, Roman could reveal how universal this pattern truly is and how common planetary systems like our own might be throughout the galaxy.
"Roman will be especially powerful because it will observe hundreds of millions of distant stars, letting scientists compare faraway planet populations to those found nearby," said Robby Wilson, a postdoctoral fellow at NASA Goddard. The telescope represents not just a tool for discovery, but a chance to finally see the full diversity of worlds that share our galaxy.